Method of coating fluorescent lamps



g- 19, 1952 E. F. LOWRY r AL 2,607,706

' METHOD OF COATING FLUQRESCENT LAMPS Filed April 50, 194'? Andrew E /lace ATTORNEY F 3 Erwin Ezowr Patented Aug. 19, 1952 Erwin F. Lowry, Lynn, and Andrew Y. Mace, Marblehead, Mass, assignors tofSylvania E1801 tric Products Inc., Salem, Mass., a

of Massachusetts corporation Application April 30, 1947, Serial No. 744,994 2 Claims. (01. 117-335) This invention relates to electric lamp coating apparatus and more particularly to apparatus for spraying coating of luminescent material to the inner wall of an elongated glass envelope.

An object of this invention is to provide a method of and apparatus for spraying a suspension of luminescent material on the innerwall of an elongated glass envelope.

Another object of this invention is to provide a method of and apparatus for spraying a suspension of luminescent material on the inner Wall of an elongated helical glass envelope from which an electric lamp may be fabricated.

Further objects, advantages and features will be apparent from the following specification when read in conjunction with the accompanying drawing in which:

Figure 1 is a perspective view of the apparatus of our invention.

Figure 2 is an exploded sectional view of a nozzle which we have employed with the apparatus of our invention. 7

Figure 3 is an enlarged plan view showing how the nozzle is mounted on the spray gun.

In the manufacture of conventional fluorescent lamps of the linear type, the elongated tubular glass envelope is provided with a coating of fluorescent materialon the inner Wall thereof. This coating is usually applied by flushing the envelope with a body of the fluorescent material. This is accomplished by positioning the elongated tube substantially perpendicular to the horizontal and introducing the body of fluorescent material either from the top or the bottom thereof. In either case the quantity of fluorescent material with which the envelope is flushed is considerably greater than the quantity which actually remains on the wall of the envelope. This excess is permitted to drain from the envelope.

Although the flushing method has proved satisfactory in coating elongated linear glass envelopes, we have found that it leaves much'to be desired when the article to be coated is non-linear or curved, such as a helical glass envelope, for

example. One of the problems which is presented in trying to flush coat a helical glass envelope is the attainment of a smooth, even coating. When a helical glass envelope is flush coated, the deposited coating, which drains as it dries, follows an irregular and uncontrollable course. This results in streaky, uneven coating, which is very undesirable. We have, therefore, developed a. methother end thereof.

, od of andapparatus for spray coating the wall of the envelope with a suspension of luminescent material. 1 j I g The apparatus of our invention comprises a drum I mounted on a shaft 2 which is supported at its ends by bearings 3 and standards 4 which are mounted on a base 5. Provisionis made to slidably mount the drum I on theshaft 2 by providing a sliding fit between a keyway 6, in the drum and an elongated key I on the shaft. "A cam 8 in the form of a single turn helix, the'pitch of which corresponds to the pitch of the elongated glass envelope which is to be coated, 'is mounted on the periphery of .the'drum adjacent one end thereof. A pair of cam followers 9,'which engage the cam 8, are supported in a standard ID. A plurality of spring clips I I, adapted to hold an elongated helical glass envelope I2 are disposed about the periphery of the drum I adjacent the As mentioned above, the apparatu'sof our'invention is designed to. permit the envelope l2 to be spray coated with a suspension of luminescent material. A spray gun I3 is employed to apply the coating to the inner Wall of the envelope I2. The gun It comprises an elongated helical barrel l4, the pitch of which corresponds to the pitch of the envelope I2, and a nozzle I5 disposed at one end of said barrel. The other end of the barrel I4 is connected, through line I6, to a supply of luminescent material suspension. The gun I3 is supported by bracket H. H

In preparing the apparatus of our invention for the spraying operation, the position of the drum I is adjusted so that an end of the envelope [2, which is mounted thereon and held by clips II, is aligned with the nozzle I5 and then the drum I is rotated to thread the envelope I2 about the gun I3 until the nozzle I5 is disposed adjacent the other end of the envelope. The relative disposition of the envelope I2 and the cam 8 is such that when this operation is performed the cam 8 will be engaged continuously by its followersffi. This arrangement insures the proper threading and withdrawal of the envelope I2 because the path described when the drum is rotated will be-the same .each time the operation is performed.

The actual spraying operation is performed by introducing a body of luminescent material suspension under pressure into the gun I3 and causing it to issue from the nozzle 15. While the spray of coating is being deposited on the inner wall of the envelope l2, the drum l is rotated in a direction opposite to the direction in which it was rotated to thread the envelope l2 over the gun l3. Thus the envelope I2 is gradually withdrawn from the gun while it is being coated. When the envelope 12 has been rotated to a position where it has been withdrawn from the gun, the flow of fluorescentimaterial suspensionrfrom. the gun-.is cut offaandv the coated .envelope .is removed from the drum.

The shaft 2 is driven by a motor [8 to which it is connected through a chain 19- :and. a.-;-reduction box 20. The flow of the suspension of fluorescent material from a reservoir 2| to the gun 13 may be controlled by a suitable valve 22. The

body of fluorescent material suspension inuthe" reservoir 2! is placed under a pressure of about 70 to 80 pounds per square inch for bestresults in atomizing the coating material as it is emitted by the nozzle I5. Air under pressure is supplied to the reservoir 2| through line 23.

As mentioned above; the suspension of luminescentmaterial is' atomized and sprayed onto v"the wall of "the glass'envelope. In changing from conventional"flush-coating-methods to a spraying system we have found that some nozzlesof 'the .type employedin flush coating systems do not perform satisfactorily. "We have also foundthat a fchange was desirablein the fluorescent malgte'rial suspension.

FA spray inozzleof the type whichwe have .found td give very'satisfactory results is shown in Figure 2. -'The nozzle l comprises a plug .24, a mixer 25 anda head 26. The mixer 25 is se'atedin a chamber 21 in the head 26'and the plug 24 is screw-threaded into the end of the ;.head. "The plug 24is provided with an elongated aperture 28 therein which extends from end to .end thereof along its longitudinah axis. The plug"24- is, provided-with a rounded head 29 .which fits into a 'chamber 30 in an end of the mixer'25. The 'wall of mixer25 which defines the chamber 30 is providedwith two apertures 3|.therein. ,The head26 is provided with an .aperture 32 in theifrontend thereof.

' .Eigure 3 .shows amannerin which the nozzle vIiil'ajrnayloe mounted on the end 'of barrel '14 of "'fthelgun l3. We have found'it advantageous to .use a ball and socket joint in mounting the noz- Qizle. on the end of the gun barrel. "Thenozzle .'Il5 is screwed into, a collar 33 on the ball por- .tion of the .joint. The ball is-seated in a nut 35, Whichisthreadedinan adapter- 36 on the end of the barrel [4. The ball 34 is provided with a holewhi'chiextends therethrough to pernmitthe flow of fluorescent coatingmaterial'from Lthe' barrel M to the'nozzle [5.

The coatingmaterial as it flows from the-barrel I4 through. the nozzle ISL-passes through the ..aperture28 in thejplug 24 into the chamber 30 in the mixeri25. The coating material passes outof chamber 30. through apertures 3| therein and Iflows alongthe outside wall of the mixer .25. tQthelhead 31 thereof. The head 31 maybe .urlderout to provide a swirling action as the coating material passes ,through the chamber 21 inlthellead 26 and into the aperture 32' there- ;in, from .whichpoint it.is emittedin asprayionto the wall. of .theglass envelope.

Spraying cannot be done satisfactorily with .fluorescent. suspensions of the type which. has

,ithe tube.

been employed successfully in flush coating systems because the spray deposition requires special physical properties, such as a very low viscosity and a delicate balance of drying properties to insure sufficiently rapid drying to eliminate the necessity for rotation of the envelope after spraying, yet assure proper leveling to obtain a coating of good appearance and high efficiency.

The fluorescent coating material which we have found to give good results comprises an organic binder material dissolved in a low boiling solvent plus a small percentage of .a solvent having a; slightly higherboiling pointga plasticizer sufficient to impart desirable properties to the dried binder film, and the finely divided inorganic phosphor which it is desired to add to Satisfactory coatings have been obtained when the viscosity of this coating suspension is between'about 10 to 50 centipoises, 20

as compared to viscosities of the order of 100-400 centipoises which have been used in flush coating systems.

The vehiclecomprises about 80.7% of methylene chloride, about 5.3% of methanol, about 5% ethylcellulose and about 9% dimethylphthalate, all percentages being by weight. The Viscosity of this vehicle-may be adjusted Withsolvent A which comprises about 90% methylene "chloride and'about 10% -methanol, these percentages-being by volume. A concentrated phosphor suspension is then'prepared by' milling, in

a ball mill forexample, about 1000 grams of fluorescent powder with-about 1700 cc. -of-the above-mentioned vehicle which has been adjusted to a viscosity of-about 42 centipoises-with the above-mentioned solvent A. I The phosphor suspension from themill is then adjusted for spraying with solvent Bwhich comprises about 66.7% normal pentane and 33.3% methanol, (the percentages being-by volume) until the'viscosity of the -mixture has been corrected to the 10+50 centipoises range mentioned above. *We have found about 22 centipoises to give verygood re-- "sults. A further adjustment is then made with the vehicle mentioned and describedabove-to lower the specific gravity ofthe mixtureto about "between 0.980 and 1.000.

What we claim is:

'1. The method of spraying a suspension of fluorescent "material on the inner wall 'of'an elongated substantially helical glass envelope,

threading said envelope over an elongatedfixed spray gun; in-

"troducing a suspension'of fluorescent material into said spray gun and forcing a spray thereof 'to be emitted by said gun and be deposited on the-inner wall of said envelope; graduallywithj drawingsaid envelope as the gun deposits a suspension of fluorescent material on the inner wall thereof; and holding said envelope against relative rotation, with respect to said spray-gun 'in' a plane transverse to said spray gun during *said withdrawal of said envelope.

2. The method of spraying a suspension of fluorescent material on the inner wall of an elongated substantially .helical glass envelope,

said method comprising: mounting said envelopev on a I support threadingsaid A envelope over i an elongated fixed spray: gun=by rotating-said support; introdu'oinga; suspension of fluores cent 'material into said spray "gum-forcing a spray'of said fluorescent materialsuspension to 'be emitted by said gun'and uponthe' inner 'wall'of'said envelopeyrotatingsaid support in a'reverse'di- REFERENCES CITED The fo11owing..-references are of record in the file of this patent:

Number 6 UNITEP STATES PATENTS i Name Date A stin May 13. 1930 alnnon Nov. 21, 1933 "gs et a1 Apr. 23, 1935 Sjulding Jan. 31. 1939 Pefikins Aug. 8, 1939 fPe'iarce Mar. 5, 1940 1 1a rden et a1. Dec. 14, 1943 'Denore May 16, 1944 eenbowe et a1. Dec. 23, 1947 

1. THE METHOD OF SPRAYING A SUSPENSION OF FLUORESCENT MATERIAL ON THE INNER WALL OF ALL ELONGATED SUBSTANTIALLY HELICAL GLASS ENVELOPE, SAID METHOD COMPRISING: THREADING SAID ENVELOPE OVER AN ELONGATED FIXED SPRAY GUN; INTRODUCING A SUSPENSION OF FLOURESCENT MATERIAL INTO SAID SPRAY GUN AND FORCING A SPRAY THEREOF TO BE EMITTED BY SAID GUN AND BE DEPOSITED ON THE INNER WALL OF SAID ENVELOPE; GRADUALLY WITHDRAWING SAID ENVELOPE AS THE GUN DEPOSITS A SUSPENSION OF FLUORESCENT MATERIAL ON THE INNER WALL THEREOF; AND HOLDING SAID ENVELOPE AGAINST RELATIVE ROTATION, WITH RESPECT TO SAID SPRAY GUN IN A PLANE TRANSVERSE TO SAID SPRAY GUN DURING SAID WITHDRAWAL OF SAID ENVELOPE. 